Interaction of the thallium cation with 1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6: Experimental and theoretical study

From extraction experiments and gamma-activity measurements, the extraction constant corresponding to the equilibrium Tl+ (aq) + 1.Cs+ (nb) double left right arrow 1.Tl+ (nb) + Cs+ (aq) taking place in the two-phase water-nitrobenzene system (1 = 1,3-alternate-25,27-bis(1-octyloxy)calix[4]arene-crown-6; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as log K-ex (Tl+, 1.Cs+) = -2.1 +/- 0.1. Further, the stability constant of the 1.Tl+ complex in nitrobenzene saturated with water was calculated for a temperature of 25 degrees C: log beta(nb)(1.Tl+) = 11.6 +/- 0.2. Finally, by using quantum mechanical DFT calculations, the most probable structures A and B of the cationic complex species 1.Tl+, which are obviously in a dynamic equilibrium, were indicated. In both of these structures of the resulting 1.Tl+ complex, the "central" cation Tl+ is bound by eight strong bond interactions to six oxygen atoms from the 18-crown-6 moiety and to two carbons of the respective two benzene rings of the parent ligand 1 via cation-pi interaction. (C) 2013 Elsevier B.V. All rights reserved.